Disclosed herein is a photosensitive copolymer and a photoresist composition which includes the copolymer.
Design rules for advanced generation microlithography (i.e., beyond 193 nm immersion lithography and into next generation optics such as e-beam, X-ray, and extreme ultraviolet (EUV) lithography operating at a very short wavelength of 13.5 nm) are trending toward smaller and smaller dimensions, for example, 30 nm and below. In general, depth of focus (DOF) necessarily decreases with higher resolution due to the higher numerical aperture (NA) and therefore resist thickness also decreases commensurate to the smaller and smaller feature sizes. With narrower linewidths and thinner resist films, consistency issues such as line width roughness (LWR) and resolution take on increasing significance limiting the performance and usefulness of photoresists. These phenomena are of interest in the fabrication of semiconductor devices; for example, excessive LWR can lead to poor etch and lack of linewidth control in, for example, transistor and gate architecture, potentially causing short circuits and signal delay.
U.S. Patent Application Publication No. 2009/0202946 discloses polymers for use in photoresists based on hydroxystyrene-containing copolymers having low activation energy (i.e., acetal and/or ketal) acid-sensitive groups, or (meth)acrylate based copolymers having bulky cycloalkyl acid-sensitive groups, which further include functionality (such as aliphatic hydroxy groups or lactone moieties) to provide surface adhesion properties. For certain acetal groups, photoresists including the exemplary copolymers disclosed in the '946 application exhibit fine pattern imaging, desirable sensitivity and exposure latitude, as well as aging stability; however, no LWR performance or improvement in LWR is disclosed.
Polymers with PAGs bonded to them provide desirable imaging properties. However, the presence of polymer bound PAG can also introduce very high polarity in and swelling of the photoresists, which can in turn introduce low mechanical strength and photoresist failure by pattern collapse for critical dimensions (CD) at narrow linewidths of 30 nm or less.